William Aikman was born in Cairnie, Scotland, in 1682 the only son of the Laird of Cairnie, Forfar. He was destined to study law but his early talent for painting led to a change of course. After spending three years studying under Sir John de Medina he sold the family estate and traveled to Italy, where he spent a further three years, then to Turkey and back to Scotland via Rome and Florence. He settled in Edinburgh in 1712 and was the best portraitist there of the time, the Scottish equivalent of Jervas and Richardson. His sitters depict most of the nobility, gentry and lawyers of the time. In 1723, about the time of the death of Kneller, he moved to London with the encouragement of the Duke of Argyll where he was not only patronized by the Scots, but became well known in literary circles and the friend of Pope, Gray, Thompson and others. He was also a close friend of the great Scottish portrait painter Allan Ramsay whose portrait he painted. In 1730 he was commissioned to paint the Royal family by Lord Burlington.
He died at his house in Leicester Fields, London, and was buried at Grey Friars Church in Edinburgh.

Works by the artist are in the following collections: Scottish National Portrait Gallery; National Portrait Gallery, London; British Museum; University of Edinburgh; Uffizi Gallery, Florence.